Underwater towed video: a useful tool to rapidly assess elasmobranch populations in large marine protected areas

Elasmobranch stock assessment studies are usually made through fisheries surveys data. However, in large marine protected areas (MPAs) the use of destructive techniques must be dismissed in order to avoid population impacts. In 2005, while conducting a marine habitat survey in two marine Special Areas of Conservation (Sebadales de Playa de Inglés and Franja Marina de Mogán) in south Gran Canary Island (Canary Islands, Spain) with underwater towed video (UTV) and underwater visual census (UVC) transects, we recognized the opportunity rose to assess elasmobranch populations through UTV. Number of observed species and specimens, overall field work effort and total surveyed area were determined and compared between methods. Mean observations per day per unit of time (MOPUT) and mean observations per day per unit of surveyed area (MOPUA) were also compared through Mann–Whitney rank sum statistical test (α = 0.05). Data analysis demonstrated that UTV is a very useful tool to rapidly assess elasmobranch populations in large MPAs in good visibility underwater environments. It can assess larger areas than UVC with the same effort (statistically significant difference found for the MOPUT; p =< 0.001), leading to more observed species (5 vs 2) and specimens (46 vs 3) per day of work, with no loss in resolution power (MOPUA values were not significantly different between UTV and UVC; p = 0.104).     

A study of heavy metals and their fate in the composting of tannery sludge

Tannery waste is categorized as toxic and hazardous in Malaysia due to its high content of Cr (in excess of 500 mg/kg) and other heavy metals. Heavy metals, when in high enough concentrations, have the potential to be both phytotoxic and zootoxic. Heavy metals are found as contaminants in tannery sludge. This investigation aimed to identify the fate of chromium, cadmium, copper, lead, and zinc concentrations in tannery sludge throughout a 50-day composting cycle. The results of this study showed a general increase in the removal of Cr, Cd, Pb, and to a much smaller extent Zn and Cu, manifested by a decrease in their overall concentrations within the solid fraction of the final product (the decreases were likely the result of leaching). Furthermore, in using a sequential extraction method for sludge composting at different phases of treatment, a large proportion of the heavy metals were found to be associated to the residual fraction (70-80%) and fractions more resistant to extraction, X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of the metals were bound to bioavailable fractions X-(KNO3+H2O).     

Multivariate analysis of the bentho-demersal ichthyofauna along soft bottoms of the Eastern Atlantic: comparison between unvegetated substrates,seagrass meadows and sandy bottoms beneath sea-cage fish farms

By means of multivariate techniques, we studied: (1) the differences in the structure of bentho-demersal, non-cryptic, fish assemblages associated with unvegetated sandy substrates, vegetated meadows constituted by the seagrass Cymodocea nodosa and the bottoms under the influence of sea-cage fish farms; as well as (2) the persistence of these patterns with regard to different scales of spatial variability, across three islands of the Canarian Archipelago (Central East Atlantic). Our sampling strategy (involving three islands, with five locations per island, and two sites within each location) detected significant changes in the composition and structure of the fish assemblages between the three habitats. Fish assemblages associated with the unvegetated and vegetated bottoms were similar among the surveyed islands. In contrast, we observed a significant inter-island variability in the fish populations associated with the sea-cage fish farms. The presence of the sea-cage fish farms increased the overall fish abundance (184.8±49.8 ind 100 m⁻²) as compared to both the vegetated (38.8±9.7 ind 100 m⁻²) and unvegetated habitats (1.1±0.4 ind 100 m⁻²). Differences within and between the habitats were found to be associated with the relative abundance of a few fish species. The most abundant species were Xyrichthys novacula in the unvegetated bottoms and Diplodus annularis, Spondyliosoma cantharus and Mullus surmuletus on the seagrass meadows. Finally, we recorded an increase in the abundance of Heteroconger longissimus, Trachinus draco and Pagellus acarne in the bottoms beneath the sea-cage fish farms. These species, in addition to a group of large benthic chondrichthyes, were responsible for the differences between islands in the composition and structure of the demersal ichthyofauna beneath the sea-cage fish farms.     

Study of metals concentration levels in Patella piperata throughout the Canary Islands, Spain

In order to assess the extent of metal contamination at rocky shores of the Canarian Archipelago, metal concentrations have been measured in Patella piperata (Gould, 1846), using the standard atomic absorption spectrophotometer technique. Ranges of elements concentrations measured (in μg g⁻¹) found in the biota were: Cd (0.36 ± 0.26 μg g⁻¹ dry wt.), Cu (2.05 ± 0.91 dry wt.), Pb (1.57 ± 1.14 μg g⁻¹dry wt.) and Zn (10.37 ± 4.60 μg g⁻¹ dry wt.). Variation in metal concentrations in Patella, was tested by using non-parametric statistical methods. Cd content had a maximum in the Archipelago Chinijo, northward of Lanzarote Island. The metal concentrations recorded at the clean stations may be considered carefully if they are used like background levels.